Cold plates are used for cooling electrical components in large scale electrical devices such as computers. The cold plate typically is cooled or chilled by a flow of refrigerant, either chilled water or a super-cooled gas or liquid.
Cold plates typically are engaged in surface-to-surface contact with a planar surface of an electronic module or an electronic chip and thus serve as a heat sink for the thermal energy generated within the electronic component. The electronic devices are contained within a low level vacuum container; and accordingly, conduction is the only significant form of cooling for the electronic components. The removal of the atmosphere from the interior of the vacuum container or thermally conductive module eliminates the possibility of convection, and the resulting overheating would cause the electronic components to malfunction prior to an adequate radiant cooling temperature being obtained. Accordingly, with no convection cooling, the electronic components must be conductively engaged with a cooled heat sink. In order to assure adequate surface-to-surface contact as well as an efficient conduction path for the heat from the electronic components to the cold plate, pistons are inserted into blind holes of the cold plate such that the pistons may be urged to engage the electronic component to provide an enhanced conductive path to the cold plate. The cold plate is provided with a plurality of blind holes into which the pistons may be fitted. In order to overcome the thermal conduction resistance of the interface between the pistons and the cold plate, it has become customary to utilize a thermal paste which has a high conductivity and which will engage both the piston surfaces and the cold plate surfaces. Thereby, the thermal barrier between the cold plate and the piston is reduced, if not eliminated.
When pistons are inserted into blind holes in the cold plate together with the thermal paste, air typically is trapped within the blind hole together with the thermal paste. This creation of uneven thermal conduction from the piston to the cold plate, caused by the entrapped air, at least partially defeats the thermal conductivity of the paste layer.
Further, the inclusion of air within the assembled pistons and cold plate assembly creates further problems when the thermal conduction module is fully assembled and then evacuated. The trapped air bubbles will expand and create pressure against the piston in excess of that designed for the assembly; with leakage over time, the air will degrade the quality of the vacuum within the thermal conduction module, possibly to the point where the module will no longer function properly. Additionally, the expansion of the air bubble will increase forces by the piston onto the electronic module or chip; if large enough, these forces might damage the electronics.